Method for compacting metal powder



Dec. 22, 1964 J. H. LUND ETAL 3,162,708

METHOD FOR COMPACTING METAL POWDER Filed June 21. 1961 20 i i I I l I lI l I g Inventors J. A. H. LUND V/LN/S S/LINS Attorney United StatesPatent 3,162,703 METHOD FOR (IQMPACTENG METAL PGiiEJER .lolin A. H.Land, Vancouver, British Columbia, and Viinis Silins, Edmonton, Alberta,Canada, assignors to Sherritt Gordon Mines Limited, Toronto, Untario,Canada, a company of Canada Filed June 21, 1961, Ser. No. 113,732 2Claims. (Ci. 264-4111) This invention relates to the utilization of animproved roll construction for roll compacting metal powders into metalrods, sheets, strips, wire and the like.

Metal powder is compacted initially into a green shape, such as in theform of sheet or strips, by feeding it, usually at a predetermined,uniform rate, into the roll gap of a pair of oppositely positioned,horizontally disposed, pressure rolls. The rolls are spaced to produce aself-supporting, partially densifled green shape of desired thickness.

There is a problem in rolling metal powder by this method if the metalpowder, during compaction, is not confined along the outside edges ofthe rolls in that metal powder tends to flow or leak from the edges ofthe rolls with the result that the longitudinal edges of the strip arenot compacted to the same density, coherence and thickness as is thecentre portion. Thus, compacted shapes formed without some provision forconfining the powder metal within the roll gap must be trimmed along theedges, thus necessitating an additional step in the overall process andresulting in the production of an appreciable percentage of wastematerial in addition to non-uniformity in the physical characteristicsof the product across its width.

Devices are known and used for confining the powder metal within theroll gap and thus preventing flow or leakage from the ends of the rolls.For example, flanges or discs of greater diameter than the roll on whichthey are mounted have been provided at the ends of one of the rolls, ora flange has been provided at one end of one roll and at the other endof the other roll. These flanges are pressed tightly against theopposing faces of the rolls and serve to confine the metal powder withinthe roll gap but they tend to create a further problem. The compactedshape tends to become wedged between the flanges and is diflicult todischarge from the rolls. Attempts to overcome this wedging effect bydrawing the compacted shape from the rolls results in distortion andbreaking of the sheet or strip.

We have found that the problems of confining the metal powder to theroll gap and preventing leakage of metal powder from the ends of therolls and of discharging the compacted shape from the rolls withoutdamage either to the physical characteristics of the shape or to thelongitudinal edges can be overcome by mounting a flange, of greaterdiameter than the roll, at each end of one of the rolls or at one end ofone roll and at the opposite end of the other roll, but spaced a shortdistance from each opposing end of the roll so that there are relativelynarrow spaces between the ends of the rolls and the opposing flanges.

In the operation of the roll compacting unit, in one modification of theinvention, some of the powder fed to the roll gap flows into and fillsthe space defined between the inner face of the flanges and the ends ofthe roll to which they are attached to the level of the surface of theroll and provides, in effect, an extension of the roll surface to theflanges. The longitudinal edges of the strip or sheet passing throughthe roll gap rest on these narrow layers of metal particles which, ineffect, provide an opposing surface which is relatively soft andyielding as compared to the hard, unyielding surice faces of the rolls.Also, since a space of equal width is defined between the inner face ofthat portion of the flange which overlaps the unflanged roll and theopposing end of this roll, the outer longitudinal edge of the strip issubjected to smaller compacting forces than the rest of the strip. Theresult is that the strip has an edge which, though quite regular, has arelatively friable border which crumbles readily thus allowing easy exitof the compacted strip from between the flanges. In an alternativemodification of the invention, the yielding or slightly resilient effectcan be provided along the longitudinal edges of the strip or sheet byfilling the spaces between the opposing ends of the rolls carrying theflanges and the inner face of the flanges to the level of the flangecarrying roll or rolls with a resilient or yielding material such asrubber. The combined effect of the layer of metal particles or theresilient material at the ends of the rolls and the open ended spacebetween the outer ends of the unflanged rolls and the inner faces of theflanges is that the longitudinal edges of the strip or sheet are notcompacted to the same degree of density or coherency as is the main bodyof the shape and constitute lines of weakness which permit, in effect,the main body of the shape to be torn evenly along the lines of weaknessat the marginal edges as it is discharged from the rolls. Thus, theshape leaving the rolls is of substantially uniform thickness, density,and coherency between its longitudinal edges and requires onlysuperficial trimming along its edges during subsequent conventional hotand/or cold working procedures.

An understanding of the utilization of the improved metal powdercompacting rolls of this invention can be obtained from the followingdescription, reference being made to the accompanying drawings in which:

FIGURE 1 is a perspective view of a pair of metal powder compactingrolls which incorporate an embodiment of powder metal confining flangesof this invention;

FIGURE 2 is a top plan view;

FIGURE 3 is an end elevation; and

FlGURE 4 is a front elevation of a modification of the invention inwhich a flange is mounted on a roll shaft of one of the rolls and theother flange is mounted on the roll shaft at the other end of the otherroll.

Like reference characters refer to like parts throughout the descriptionand drawing.

Referring to the modification of the invention illustrated in FIGURES lto 3, a flange is provided at each end of one of the rolls. It will beunderstood that one of the flanges can be mounted on the roll shaft ofone of the rolls and the other flange can be mounted on the roll shaftat-the opposite end of the other roll as illustrated in FIGURE 4.

Referring to FIGURES l to 3 of the drawing, the numerals 22 and 23indicate rolls of a conventional type used for compacting metalparticles. In the modificaticn illustrated, they are plain, orunproflled rolls, adapted to compact the metal particles into sheet orstrip of a desired width. The rolls are mounted on shafts 25-25a whichare driven according to conventional practice, such as by an electricmotor through a train of speed reducing gears. The rolls are formed ofconventional material such as steel and, conventionally, are adjustablymounted to apply a pressure on the particulate material fed into theroll gap or the space 27 between the rolls, with provision to increaseor reduce the roll gap to increase or reduce the thickness of thecompacted sheet or strip. Using smooth, hard, ground steel rolls sixinches in diameten'metal strip from 0.02 to 0.04 inch in thickness wasobtained with pressures estimated at up to about tons per square inch.

Methods and apparatus are known and are in use 3 for feeding metalpowder to the roll gap at a relatively uniform rate and do not form partof this invention.

The numerals -21 indicate discs or flanges, as illustrated in FIGURES lto 3, one of which is mounted on each end of roll shaft adjacent to butspaced a short, predetermined distance from the opposing end of the roll22 leaving spaces 2442411 between the opposing faces of the flanges21-2ti and the ends of the rolls 22, 23.

The flanges or discs 20-21 are formed of steel or other rigid materialcapable of withstanding the lateral force of the metal particles appliedagainst their faces in the operation of the rolls. The radius of theflanges is greater than the radius of the rolls, at least to the extentof the width of the roll gap during operation, for example, from about0.5 to about 1 inch greater, depending on roll radius and on the widthof the roll gap.

The flanges can be adjustably secured to the roll shaft 25 by anyconventional means which will hold them securely in their predeterminedpositions relative to the opposing faces of the ends of the rolls. Inthe modification illustrated in FiGURES 1 to 3, the flanges are formedwith outwardly extending hub portions 3944041 which are drilled toreceive set screws SL315; by means of which the flanges are rigidlysecured in their predetermined positions.

The flanges are adjusted on the roll shaft to leave gaps or spaces 2424aof predetermined width between the opposing faces of the flanges and theends of the rolls 22, 23. The width of the spaces depends on the sizeand the flow characteristics of the metal particles being compacted. Ifthe gap is too wide relative to the particle size of the metal powderbeing compacted, powder will pass between the ends of the working facesof the unflanged roll (23 in FIGURES 1-3) and the inner face of theflanges 20, 21 too rapidly and very low or no compaction pressures atall are developed along the edge zone. If, on the other hand, the gaps24, 24a are too narrow, powder particles may jam in the space betweenthe end of unflanged roll 23 and the inner face of the flanges 20, 21.This may impede the smooth operation of the equipment or result inextremely high compaction forces at the edge zones with the result thatthe compacted strip emerging from the mill jams between the flanges. Wehave found that the distance between the opposing faces of the ends ofthe rolls and the flanges should be at least about 0.001 inch and verysatisfactory results have been obtained within the range of from about0.001 to 0.05 inch when roll compacting, relatively free flowing metalparticles of from submicron to about 150 microns in size. As the flanges20-21 are adjustable on the shaft, the spaces can be readily determinedfrom which the best results are obtained in compacting a particularmetal powder and the flanges secured to the shaft accordingly innon-yielding relation.

FIGURE 4 illustrates a modification of the invention in which a flangeis mounted on a roll shaft adjacent to but spaced a short distance froma roll 42. The other flange 43 is mounted on the other roll shaft 44aadjacent to but spaced a short distance from the other roll 44. Theflanges 40-43 are mounted on the shafts 45 and 44a in the mannerdescribed above. Provision can be made to remove the particles trappedin the spaces 24-24a during the rotation of the rolls after thedischarge of the compacted strip or sheet, such as by a high pressureair blast, as indicated by the numeral 35, FIGURE 2, or by a stationarytool, not shown, which dislodges the particles trapped in the space.Thus, the beds of particles in the spaces are continuously replaced andthey do not become compacted to the extent that they expose hard,unyielding surfaces to the layer of particles along the marginal edgesof the layer of particles in the roll gap.

In the modification of the invention illustrated in FIG- URE 4, aresilient material 41, such as a strip of rubber, is inserted in each ofthe spaces 50-50a. between the opposing faces of the ends of the rollsand the flanges. The resilient material fills the spaces to the level ofthe roll surface and, possibly, a little higher. The layer of metal ormetal coated particles which rests on these resilient surfaces is notcompacted to the same extent as is the main body of the shape and thusform lines of Weakness along which the main body of the shape isseparated as it is discharged from the roll gap. This modification hasthe advantage that no particles enter the spaces and it is not necessaryto clean them during the rotation of the rolls after the discharge ofthe compacted strip or sheet from the roll gap.

The improved metal powder compacting rolls of this invention have beenfound to have important advantages. The flanges serve to confine thepowder in the roll gap which, in effect, extends between the opposingfaces of the flanges. However, the roll surfaces are hard and unyieldingwhile the surfaces of the beds of particles trapped in the spaces 2424aare yielding. Thus, the strip or sheet formed in the gap which extendsthe length of the rolls is strongly coherent and is of substantiallyuniform thickness and density while the portion which extends betweenthe ends of the rolls and the flanges is substantially less dense andcoherent. Thus, in discharging the strip or sheet from the rolls, ittears easily along the lines of weakness at its less dense and lesscoherent edges. As a result, there is no damage to the main body of thestrip or sheet in discharging it from the rolls and only a very minoramount is lost in the edge trimming operation. Particles which collectin the spaces between the opposing faces of ends of the rolls and theflanges can be dislodged during the rotation of the rolls or they can beprevented from entering the spaces by filling them with a resilientmaterial such as rubber. A further important advantage is that it hasbeen found in the operation of the rolls that they tend to movelaterally slightly relative to each other, as indicated by the arrows,FIGURE 4. This causes binding of the ends of one of the rolls and theopposing face of one of the flanges, depending on the direction ofmovement, when the flanges are fixed tightly against the end of therolls, with resultant wear on the face of the roll. This binding effectcan be reduced, if not completely overcome, by mounting the flanges inthe manner illustrated in FIGURES 13 and it can be overcome completelyby determining the normal direction of the lateral movement by operationof the rolls and then mounting the flanges, one on each of the rollshafts, as illustrated in FIGURE 4, so that each roll can move laterallywithout binding at either end against an opposing face of a flange.

It will be understood, of course, that modifications can be made in theembodiments of the invention described and illustrated herein withoutdeparting from the scope of the invention defined by the appendedclaims.

What we claim as new and desire to protect by Letters Patent of theUnited States is:

1. The method of compacting metal powder into elongated strips whichcomprises feeding finely divided metal particles to a roll gap definedbetween two rotatable rolls of a roll compacting unit, confining themetal powder at the ends of the roll gap by means of circular flangesadjustably mounted on a roll shaft at each end of the rolls adjacent tobut in spaced relation to the opposing faces of the rolls leaving spacestherebetween, compacting the longitudinal edges of the strip on yieldingsurfaces at the ends of the rolls formed of particles forced into saidspaces and thereby forming lines of weakness between the main body ofsaid strip and the longitudinal edges thereof, and discharging thecompacted strip from the roll gap.

2. The method of compacting metal powder into elongated strips whichcomprises feeding finely divided metal particles to a roll gap definedbetween two rotatable rolls of a roll compacting unit, confining themetal powder at the ends of the roll gap by means of circular flangesadjustably mounted on a roll shaft at each end of the rolls adjacent tobut spaced between 0.001 inch and 0.05 inch from the opposing faces ofthe ends of the rolls leaving spaces therebetween, compacting thelongitudinal edges of the strip on yielding surfaces at the ends of therolls formed of metal particles forced into said spaces and therebyforming lines of Weakness between the main body of said strip and thelongitudinal edges thereof, and discharging the compacted strip from theroll gap.

Hilgerd Oct. 24, 1876 Hohne et al Apr. 26, 1887 6 Sims Feb. 18, 1890Ncvegold Oct. 6, 1891 Longanesi Dec. 30, 1924 McConouglley Aug. 23, 1932Smith Aug. 27, 1935 Blume Feb. 4, 1936 Johnson Apr. 2, 1946 Fe-ther Apr.10, 1951 Cofek Nov. 5, 1957 Heck Sept. 22, 1959 Melville et al. Apr. 19,1960 Dasher Nov. 28, 1961 Leib et a1. Apr. 2, 1963 FOREIGN PATENTS vItaly Of 1926

1. THE METHOD OF COMPACTING METAL POWDER INTO ELONGATED STRIPS WHICHCOMPRISES FEEDING FINELY DIVIDED METAL PARTICLES TO A ROLL GAP DEFINEDBETWEEN TWO ROTATABLE ROLLS OF A ROLL COMPACTING UNIT, CONFINING THEMETAL POWDER AT THE ENDS OF THE ROLL GAP BY MEANS OF CIRCULAR FLANGESADJUSTABLY MOUNTED ON A ROLL SHAFT AT EACH END OF THE ROLLS ADJACENT TOBUT IN SPACED RELATION TO THE OPPOSING